Silicones having hydrophilic groups exhibit excellent surface activity due to possessing both a silicone moiety, which exhibits properties such as hydrophobicity, softness, lubricity and chemical stability, and a hydrophilic group moiety, which exhibits properties such as hydrophilicity, moisture retention properties and adhesive properties. Therefore, silicones having hydrophilic groups are widely used in foods, resins, coatings, cosmetic compositions and the like, and a variety of hydrophilic silicone compounds have been known in the past. In particular, silicone oils such as low molecular weight cyclic siloxanes are often blended in order to improve the sensation during use of a cosmetic composition, and polyether-modified silicones (polyether-modified polysiloxanes) are widely used as cosmetic composition raw materials such as surfactants due to exhibiting good compatibility with silicone oils.
On the other hand, aside from polyether-modified (polyoxyalkylene-modified) silicone, glycerin-modified silicone also is known as a nonionic hydrophilic silicone (Patent Documents 1 through 9). However, there are considerable technical difficulties associated with the stable production of glycerin-modified silicone as a raw material for cosmetic compositions or external use preparations. Unsaturated group-containing glycerin derivative, a raw material of glycerin-modified silicone, is comparatively expensive and difficult to obtain on a commercial scale, and its application is limited. Furthermore, as will be discussed below, there are unsolved problems associated with the reduction of the odor of a glycerin-modified silicone.
In recent years, glycerin-modified groups have attracted attention because their oxidative stability and feeling to touch are both superior to those of polyether-modified (polyoxyalkylene-modified) groups. The applicant of the present application also proposes the use of silicones having glycerin and other hydrophilic modified groups as cosmetic composition raw materials (Patent Documents 20 and 21).
Such glycerin-modified silicone or compositions comprising the same can be synthesized by, for example, a hydrosilylation reaction between an organohydrogenpolysiloxane having a silicon-bonded hydrogen group and a glycerin derivative group-containing compound having a carbon-carbon double bond. However, glycerin-modified silicone or compositions comprising the same sometimes have an aldehyde like odor. The odor increases readily particularly because of the effects of the passage of time, the temperature, and water, so problems sometimes occur in its use in applications of external use preparations and cosmetic compositions applied to the human body. In addition, even when it is possible to incorporate glycerin-modified silicone or compositions comprising the same in an external use preparation or a cosmetic composition, there are problems such as its incorporation amount being restricted. As a result, the applicant of the present application has also proposed and specifically disclosed in the above documents that a publicly known odor reduction method and purification method such as acidizing and hydrogenation are preferable when using a silicone having glycerin or another hydrophilic modified group of the application as an external use preparation or a cosmetic composition (Patent Documents 20 and 21). These treatments were able to reduce odors and yielded silicones having a hydrophilic modified group, which was suitable for use as a cosmetic composition raw material.
On the other hand, a great deal of research into reducing the odor of polyether-modified polysiloxanes (polyoxyalkylene group-containing organopolysiloxanes) has been conducted so far. The cause of odorization over time of a polyether-modified polysiloxane that was first reported was the aldehyde and acid produced as a result of oxidation degradation (rancidity) over time of the polyether moiety in the polyether-modified polysiloxane composition. Examples of technologies to suppress this oxidation degradation include the methods recited in Patent Documents 10 and 11 in which tocopherol, phytic acid, or a similar antioxidant component is added to the polyether-modified polysiloxane composition.
However, the use of only an anti-oxidizing agent results in the insufficient suppression of the odorization over time of a formulation based on the polyether-modified polysiloxane and, as a result, other causes were investigated. As a result, Patent Document 12 recites that propionaldehyde originating from unreacted propenyl-etherified polyoxyalkylene is a cause of the odor.
The polyether-modified polysiloxane composition is typically synthesized via a hydrosilylation reaction of an organohydrogenpolysiloxane having a silicon-bonded hydrogen group and a polyoxyalkylene having an allyl ether group at a terminal. Patent Document 12 recites that, in the production of the polyether-modified polysiloxane composition, a double bond of the allyl etherified polyoxyalkylene migrates inward due to the influence of a platinum catalyst and a portion of the allyl-etherified polyoxyalkylene becomes a propenyl-etherified polyoxyalkylene and remains in the polyether-modified polysiloxane composition as is without reacting with the organohydrogenpolysiloxane. Patent Document 12 also recites that the propenyl-etherified polyoxyalkylene degrades over time, thus producing ketones and aldehydes which results in the odorization. Moreover, hydrolysis in the presence of an acid is disclosed as a useful deodorization method.
However, while this deodorization method could be thought to be useful if all of the allyl groups of the polyoxyalkylene remaining in the composition were replaced with propenyl groups, in actuality, a significant proportion of the allyl-etherified polyoxyalkylene which is not easily hydrolyzed remains. As a result, the composition cannot be sufficiently deodorized using the deodorization method of Patent Document 12. On the other hand, if a strong acid is used that can hydrolyze the allyl-etherified polyoxyalkylene, the carbon-oxygen bond at the polyoxyalkylene site and/or the silicon-oxygen bond at the polysiloxane site may disconnect, so using such an acid is inappropriate. Additionally, in order to perform the hydrolysis reaction in a quantitative manner, excessive amounts of water and acid are needed. These excessive amounts of water and acid complicate post treatment processes and, therefore, this deodorization method is not preferable.
In order to resolve this problem, methods for suppressing the production of propionaldehyde have been disclosed (Patent Documents 13 to 16). In these methods, a hydrogenation treatment is performed as a deodorization method of the polyether-modified polysiloxane composition in order to alkylate the alkenyl groups (double bonds) included in the alkenyl group-containing polyoxyalkylene (including both propenyl-etherified polyoxyalkylene and allyl-etherified polyoxyalkylene) remaining in the composition. However, even with a polyether-modified polysiloxane composition deodorized using a hydrogenation reaction, in cases where a formulation including water and an alcohol is compounded, it may be difficult to achieve sufficient deodorization over time or under elevated temperature conditions.
A cause of the odorization is acetal and similar aldehyde condensation products that are free of unsaturated bonds that remain in the composition. Thus, for the purpose of completely eliminating the acetal and other aldehyde condensation products, technology in which treatment using the acid aqueous solution and hydrogenation treatment are combined (Patent Document 17); and technologies in which hydrogenation treatment and treatment using a solid acid catalyst are combined (Patent Documents 18 and 19) are disclosed. The technology recited in Patent Document 17 is applied not only to polyether-modified silicones, but also to glycerin-modified silicones and sugar-modified silicones. That is, it is acknowledged that performing at least hydrogenation treatment is preferable in the deodorization of hydrophilic silicones as a raw material suitable for use in cosmetic products.
However, hydrogenation treatment requires dedicated special equipment and catalysts. Furthermore, silicones modified with polyhydric alcohols such as sugar and glycerin derivatives have much higher viscosities than viscosities of general polyether-modified silicones, so it is essential to dilute with a large quantity of solvent, from the perspectives of production time reduction and reaction efficiency when performing hydrogenation treatment. These are the principal reasons that the cost of polyhydric alcohol-modified silicone, which was high to begin with, has increased further, and that commercial sales of said modified silicone are stagnating.
Thus, in odor reduction treatments such as acid aqueous solution based treatments that can be performed comparatively inexpensively, it is difficult to reduce the odor of glycerin-modified silicone or a composition comprising the same, as a raw material suitable for cosmetic compositions. When hydrogenation treatment for further odor reduction is required, it generally becomes a drawback with respect to processing and cost.
Furthermore, given the cost drawback, even when hydrogenation treatment is performed by applying hydrogenation equipment such as that used for polyether-modified silicone, glycerin-modified silicone generally is highly viscous, and a solvent removal process and dilution treatment unnecessary for polyether-modified silicone, such as dilution with a large quantity of solvent, become necessary. Not only does this result in an additional cost related drawback, but there are problems related to safety and the increase in the environmental burden associated with the use of large quantities of solvent. In addition to the technical drawbacks, these are factors that further increase the costs of industrial products, with respect to environment and business management.
As a result, for the glycerin-modified silicone or compositions comprising the same, it remains technically very difficult to reduce the odor of the raw materials of cosmetic compositions and external use preparations. Furthermore, the cost increase associated with odor reduction becomes a burden, and compared with normal polyether-modified silicone, it is difficult to supply refined products with sharply reduced odor, at a low price and in large quantity. Regardless of its superior performance, it has not been widely adopted in the market, which is a problem. As a result, to have glycerin-modified silicone widely adopted in the market, there is a demand for technical development that inexpensively and simply enables a high level of deodorization of glycerin-modified silicone, without performing odor reduction treatment that uses expensive and special equipment such as hydrogenation treatment. In this regard, there is still some room for improvement in the hydrophilic silicone odor reduction treatments proposed by the applicant of the present application in the past (Patent Documents 20, 21).